The present invention relates to a secondary air induction system for an internal combustion engine of a motor vehicle comprising a turbine and a compressor, with a turbine wheel of the turbine and a compressor wheel of the compressor rotatably mounted on a common shaft inside a turbocharger housing.
As a rule, turbocharger comprise two flow machines, namely, a turbine and a compressor, which are mounted on a common shaft. An air or gas stream produced as a result of a pressure difference drives the turbine, which in turn drives the compressor, which draws in air and pre-compresses it. The shaft is normally supported by oil lubricated friction bearings.
To prevent problems during cold start and in a warm-up period of internal combustion engines in motor vehicles, the engines are provided with secondary air induction systems in the form of turbocharger. The turbine of the secondary air induction system is driven, for example, by the pressure difference across a throttle valve in an air intake channel of the internal combustion engine. The turbine, in turn, drives the compressor, which is used to introduce fresh air into the exhaust system of the internal combustion engine. The oxygen content in the fresh air stream leads to an oxidation of the pollutants in the exhaust system. In addition to the resulting removal of pollutants, the thermal energy released during oxidation heats the catalytic converter more quickly to the desired operating temperature.
With systems becoming increasingly complex and undesirably heavy and limited space available in the engine compartment, a suitable secondary air induction system must be small and light. To achieve a sufficient degree of effectiveness, it must be designed to operate at a high speed. This is associated with undesirably high noise generation In addition, the shaft bearings for the turbocharger should be independent of external lubrication.